Researchers at the University of Washington's Dog Aging Project gave rapamycin to 16 dogs and imaged their hearts.

"It started to function better. It started to look like a more youthful heart," said Matt Kaeberlein, co-director of the Dog Aging Project, who has presented this research at conferences but hasn't yet published it.

Those dogs took rapamycin for only 10 weeks.

A prescribed rapamycin to a very sick dog that had a stroke. A month after his stroke, the dog was so weak, he had to be fed by hand and carried everywhere.

But rapamycin changed all that, Anderson and Godfrey said.

"The third day after taking rapamycin, he could eat on his own. By the seventh day, he was walking on his own," Anderson said.

Sixteen months later, the dog who had been given two months to live is still alive, and while clearly old, he's still active and able to run around the yard.

A 13 year old dog was getting old and achy and losing stamina. Within days of taking the drug the dog was able run for hours, whereas before, just a 30-minute walk would tire him out.

A 14 year old Tibetan terrier given low doses of Rapamycin looks and acts younger than his 14 years, which would be around 80 or 90 in human years. There have been no side effects.

Rapamycin to tiny monkeys called marmosets and hasn't see any negative side effects for them.

The results "raise the possibility that (rapamycin) may have beneficial effects" on the decline in immune function that occurs naturally as we get older.

A researcher prefers to think in terms of treatments that will delay the onset of diseases of aging, such as dementia or heart disease. In mice, rapamycin has been shown to slow these two types of declines, as well as several others.

Over the next year, Kaeberlein will be studying rapamycin in a much larger group of dogs: about 150, compared with the 16 he studied earlier.

He said other groups are looking at doing more aging studies in rapamycin in humans,